1. Field of the Invention
This invention relates generally to methods for extending the shelf-life of food compositions and particularly to methods for extending the shelf-life of food compositions containing one or more long chain polyunsaturated fatty acids.
2. Description of the Related Art
Certain long chain polyunsaturated fatty acids (LCPUFAs) are critical nutrients for the health of an animal. LCPUFAs are increasingly known for their health benefits when included as part of an animal's diet. Since these essential nutrients cannot be synthesized from basic substrates in the body of most animal species, at least in quantities sufficient to elicit the full benefit of these nutrients, LCPUFAs or precursor LCPUFAs must be present in the animal's diet. Generally, LCPUFAs are present at low levels in the diet of many animals, including most human diets, but are completely absent from many foods.
Omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are particularly important LCPUFAs in animal nutrition. As important structural components of the central nervous system, they are critical dietary components for pregnant animals and newborns. Such LCPUFAS are thought to enhance cognitive function, particularly if consumed at an early age. Further, both EPA and DHA have reportedly been found to increase long bone density, decrease cancer risk, decrease inflammation, and increase visual acuity and retinal function in human infants. Both may also have a role in counteracting asthma and allergies and in alleviating psoriasis and arthritis. Cardiovascular benefits of consuming EPA and DHA have also been documented, including an improvement in heart rate variability in coronary patients, a decrease in blood levels of LDL (low density lipoprotein) in long term studies, and a reduction in sudden cardiac death in patients with coronary heart disease.
Marine oils have particularly high levels of EPA and DHA. High concentrations of these omega-3 fatty acids are found in oily species of fish native to cold waters, including salmon, mackerel, menhaden, sardine, halibut, cod, trout, tuna, eel, herring, and other species. Other sources of EPA and DHA include oils from seals, dolphins, whales, polar bears, plankton, krill, algae, and microbial sources.
Because of their beneficial properties, it is desirable to incorporate LCPUFAs and more specifically EPA and DHA into food compositions. However, these fatty acids are subject to rapid oxidation when exposed to air, metal, light, and/or heat during processing and storage of such compositions. Oxidation of LCPUFAs reduces the nutritional quality and palatability of a food composition and increases production costs. Further, compositions containing oxidation products of LCPUFAs can adversely affect the health and immune status of an animal when consumed.
Flaxseed and flaxseed oil are popular sources of LCPUFAs and tend to be somewhat more stable to oxidation than other sources of LCPUFAs. Flaxseed and flaxseed oil, however, are not direct sources of EPA and DHA. Flaxseed and flaxseed oil contains precursor LCPUFAs that must be metabolized in the body to produce the EPA and DHA.
U.S. Pat. No. 6,063,414 discloses a dry food high in soluble fiber that has increased palatability when packaged in gas impermeable bags versus lined or unlined paper bags. The food is said to contain flaxseed meal and to be “several times higher than most pet foods in unsaturated fatty acids which are susceptible to oxidation.” Also reported are studies of water activity, but not palatability, of the food when the atmosphere inside the bags was modified, e.g., by nitrogen flushing to reduce oxygen below 2% and/or by addition of an oxygen scavenger.
Lytle et al. (1992) Nutrition and Cancer 17(2), 187-194 discloses low temperature (<40° C.) preparation of rodent diet formulations in the form of powder or pellets containing 16% fish oil. The formulations were reportedly packaged into bags which were flushed with nitrogen and heat sealed. The fatty acid analyses of air dried pellets, vacuum dried pellets, dried powdered diet, pellets exposed to four days of air at ambient temperatures, and pellets stored for 45 days at −20° C. showed no statistical difference in overall fatty acid composition.
Analytical data from short-term studies are not necessarily indicative of longer-term shelf-life of a food composition comprising one or more LCPUFAs. Therefore, a need still exists for processes of stabilizing food compositions containing LCPUFAs, particularly food compositions containing EPA and/or DHA, such that a desired shelf-life of at least about 6 months can be attained.